This invention relates to aircraft engine ducted fan cowlings with rear thrust reverser sections mounted independently of the inner engine core cowling. Specifically, the invention is a fairing arrangement for fan shroud braces in such an environment.
In aircraft ducted fan (bypass) engines, a fan exhaust duct channels cold, bypass fan exhaust flow rearwardly, the duct being defined by an outer wall of an inner engine core cowling and an inner wall forming a continuation of the outer wall of the shroud enclosing the fan. The fan exhaust duct at its rearward section may also contain the hot engine exhaust flow in some configurations or may only contain the fan exhaust air.
The outer fan exhaust cowling is faired to reduce power plant drag, particularly where the engine is mounted under an aircraft wing or is attached to the rear section of the fuselage of an aircraft.
The rearward located thrust reverser section of the fan exhaust cowling includes thrust reverser elements of any known type, for example, doors, flaps or cascade elements. Illustrative examples of such thrust reversers can be seen in French Patent Nos. 1 482 538 and 2 030 034. In such examples, thrust reverser elements include pivoted doors forming part of the external cowling defining the fan exhaust duct when closed, a fixed upstream or forward structure, a rearward structure and longitudinal beam elements connecting the forward and rearward structures and extending between the doors. The doors are circumferentially spaced around the fan exhaust duct and pivoted between their forward and rearward ends for rotation about pivots connected to the beams on either side of the doors. The doors themselves are constructed with end, side, inner and outer walls that may constitute part of the fan exhaust duct outer wall.
An exemplary cascade type thrust reverser is seen in U.S. Pat. No. 4,145,877 where the thrust reverser includes flaps driven by a linearly movable rear shroud, the flaps effectively blocking the fan exhaust duct and directing the fan exhaust flow through cascade vanes which are exposed when the rear shroud is opened. In this example, a specific design feature is the flap driving linkage unconnected with the primary engine inner cowling.
As illustrated in FIG. 1 of the appended drawings, an outer ducted fan cowling with a split thrust reverser section 10 that can be opened in two sections 12 is combined with a primary inner engine cowling 11 covering the engine core. This type of arrangement defines a so-called C-duct 15 that carries fan bypass exhaust air rearwardly (downstream).
This arrangement enables easy engine access after a locking system holding the two halves 12 together at their bottom sides are released and each half is pivoted upwardly about a longitudinal pivot axis located near an engine pylon, the pivot axis extending above and parallel with the engine axis.
This type of cowling requires a physical link at the rear side of the cowling halves 12 called an island that connects the primary inner engine cowling 11 and outer fan exhaust cowling 12. A part of the island 13 extends into the fan exhaust stream, which is also true of the part 14 defining the C-duct at the upper section of the reverser section.
FIG. 3 shows the reverser section of FIGS. 1 and 2 in the environment of a known ducted fan type turbojet engine layout that includes fan shroud braces 3 located towards the rear of the fan shroud or enclosure 4 and that connect the shroud 4 to inner engine structural elements. The braces are located just forwardly of the rearward fan exhaust cowling and thrust reverser section 10 adjacent the upstream inlet to the duct 15.
In known fan exhaust cowling and thrust reverser systems integrated with the fan shroud or enclosure, the braces 3 can include aerodynamically shaped and contoured fairing parts located rearwardly of the braces and extending along the fan exhaust flow path in the fan exhaust duct because the supporting structure for such fairing arrangements is available in the fan exhaust cowling and reverser structure. Such aerodynamic parts, for example, can be mounted on the inner or outer walls 11 and 12. The island 13 and enclosing part 14 likewise can be formed to fair the rear sides of braces 3.
However, when the primary engine core cowling 11 is largely or entirely independent of the fan exhaust outer cowling and reverser structure 12, as shown in FIG. 4, support for the aerodynamic fairings for struts 3 at their downstream ends is not possible using the outer fan cowling and reverser structure.